TNIK, a novel activator of FAK and YAP signaling, is a therapeutic target in Lung Squamous Cell Carcinoma

Abstract

Distal chromosome 3q amplification (3q26-29, also known as the 3q amplicon) is the most frequent genomic alteration in lung squamous cell carcinoma (LSCC). Analysis of LSCC samples from the TCGA reveals that nearly 50% of LSCC patients harbor the 3q amplicon that includes the resident protein kinase gene TNIK. Recent studies have pinpointed TNIK as a potential oncogenic driver in cancer cells with distal 3q amplification; however, the therapeutic potential of TNIK remains unexplored. We found that TNIK was highly expressed in LSCC cells with the 3q amplicon, while its expression was modest in cells that lacked the 3q amplicon, consistent with data from the TCGA. To evaluate TNIK as a target in LSCC, we generated stable, doxycycline-inducible cells expressing shRNA to deplete TNIK from LSCC cells and conducted functional assays to measure cell proliferation and survival. TNIK knockdown or inhibition of its kinase activity with a small molecule inhibitor significantly diminished the viability of LSCC cells with 3q amplification in vitro and in cell line-derived xenograft mouse models. We also observed that TNIK inhibitors significantly abrogated the growth of LSCC patient-derived xenografts and showed that TNIK inhibition induced apoptotic cell death in LSCC cells that harbor the 3q amplicon. Importantly, TNIK depletion or catalytic inhibition in LSCC cells that lack the 3q amplicon had no significant effect on cell survival. Finally, we used a combination of bioinformatics and proteomic analysis (RPPA, peptide mapping, and mass spectrometry) to define the underlying mechanisms driving TNIK mediated cancer cell survival. We identified the tumor suppressor MERLIN as a novel TNIK substrate and determined that TNIK phosphorylates MERLIN at serine 13 and 315. We also show that TNIK is required to maintain FAK activation and stabilize the YAP transcription factor, two oncogenic pathways inhibited by MERLIN. In conclusion, our results demonstrate that TNIK maintains survival of LSCC cells through modulation of a novel TNIK-MERLIN-YAP/FAK signaling pathway and validate TNIK inhibitors in pre-clinical models of LSCC, including patient-derived xenografts. In summary, we have pinpointed the protein kinase TNIK as a promising therapeutic target for the treatment of LSCC patients with distal chromosome 3q amplification.